Network neighborhoods are a key communication abstraction in sensor networks, 
allowing sensor nodes to collect and aggregate sensor data from nearby other 
nodes. In many applications, multi-hop neighborhoods of several nodes overlap, 
such that nodes participate in many neighborhoods, having to contribute their 
data items to all containing neighborhoods. We consider two orthogonal 
approaches to ef ciently support this data aggregation problem. A push-based 
approach, where each node oods its data item in a multi-hop neighborhood, and 
a pull-based approach, where each node collects data from nodes in a multi-hop 
network neighborhood using a spanning tree. Our goal is to identify situations 
where one approach outperforms the other. For this, we implement these 
protocols in TOSSIM, study overhead and yield as a function of the fraction of 
nodes in the network that perform data aggregation over a multi-hop 
neighborhood, and report our ndings.